This is a continuing prospective epidemiologic study to evaluate the risks and nature of radiation-induced neoplastic disease in three irradiated populations. The three cohorts are composed of: (1) 2,872 individuals who received x-ray treatment in infancy for an enlarged thymus gland and their 5,055 non-irradiated siblings, (2) 606 women treated by x-rays for acute postpartum mastitis and 1,299 non-irradiated women who serve as a comparison group, and (3) 1,388 individuals treated by x-rays and/or intranasal radium in childhood for lymphoid hyperplasia of the nasopharynx and their 2,746 non-irradiated siblings. The irradiated subjects were treated between 1926-1960 in Monroe County in Upstate New York. The first aim is to examine radiobiological and host factors in relation to a) radiation-induced thyroid tumors in the thymus cohort and b) radiation-induced breast tumors in the mastitis cohort. Specific radiobiological factors of interest include estimates of overall excess risk, the shape of the dose-response curve, the temporal pattern of risk, and the effect of dose fractionation. In addition, the recent observation of an increased risk of tumors of the breast, bone, nervous system, salivary gland, skin, and genitourinary tract among the irradiated members of the thymus cohort will be reevaluated. To accomplish this, these two cohorts will be surveyed by mail questionnaire to obtain information on recent illnesses and relevant host characteristics. The second aim is to a) determine whether irradiation for lymphoid hyperplasia of the nasopharynx is associated with an increased incidence of benign and malignant neoplasms, and b) examine if there is a dose-response relationship for thyroid tumors. Data from a mail survey (currently in progress) of this cohort will be analyzed to address this objective. Finally, a computerized record linkage with the New York State Cancer Registry will facilitate an evaluation of the completeness of self-report of cancer using a mail questionnaire.